Wed 17 Feb 2010 – Switching passengers from air to high-speed rail on short-haul routes is a growing mantra but a new study concludes that the principal benefits of high-speed rail are time savings and additional capacity, not a reduction in greenhouse gases. Traffic diverted to high-speed rail from other forms of transport over a route of 500km would save around 90,000 tonnes of CO2 emissions a year, assuming 10 million single journeys. However, the construction emissions alone for a line of this length may amount to several million tonnes of CO2. Therefore, says the study, in cases where anticipated journey volumes are low it is not only difficult to justify investment on economic grounds, it may also be hard to defend a project for environmental reasons as it would take too long for traffic to offset the emissions caused by building the line.

High-speed rail (HSR) is fast becoming a political solution, particularly in Europe, to dealing with airport expansion, capacity restrictions and related environmental impact issues. Even in the US, HSR is attracting attention and last month the US administration announced $8 billion in grants towards its development.

However, says the study by Per Kågeson of Sweden’s Nature Associates, the cost of building high-speed lines is high, ranging from 9 to 40 million euros per km, with an average of €18m per km. Investment in infrastructure for modal shift should therefore only be considered when traffic volumes are high enough to carry the cost. Whilst there is no cause to prohibit such investment on environmental grounds, the carbon gains made in traffic should balance the emissions caused during construction, says Kågeson.

He quotes a European Commission report that said: “Only under exceptional circumstances (a combination of low construction costs plus high time savings) could a new HSR line be justified with a level of patronage below 6 million passengers per annum in the opening year; with typical construction costs and time savings, a minimum figure of 9 million passengers per annum is likely to be needed.”

The study concludes that investment in HSR is under most circumstances likely to reduce greenhouse gases from traffic compared to a situation whereby the line was not built, but the reduction is small and it may take decades for it to compensate for the emissions caused by construction. However, where capacity restraints and large transport volumes justify investment in HSR then this will not cause overall emissions to rise. With smaller anticipated traffic volumes, it may be better to upgrade an existing line to accommodate somewhat higher speeds.

“Investment in HSR cannot be expected to contribute much to climate change mitigation,” argues Kågeson. “Investment in conventional fast trains may in some circumstances be significantly more beneficial. It may be time for many environmentalists to reconsider their attitude to high-speed rail.”